The invention concerns an electronic regulation system for alternator excitation, which is capable of being added by means of connectors, or other connecting means, to an alternator already provided with its own excitation system.
As it is well known, the excitation of alternators with or without brushes, is obtained through different systems, among which the following can be mentioned:
compound excitation PA1 excitation by electronic voltage regulation PA1 mixed excitation consisting of compound and electronic regulator.
Excitation of the compound type is obtained by calculating the vectorial sum of two currents, one being proportional to the voltage of the generator terminals, the other being proportional to the phase current, and by rectifying the resulting current. Excitation by means of electronic voltage regulation is obtained by taking the voltage from the terminals at the output of the alternator, comparing it with a reference voltage and by inputting the same into the electronic regulator which supplies the power necessary for the excitation.
Mixed excitation, on the other hand, is characterized by a compound which supplies to the machine an insufficient or an excessive excitation, and an electronic regulator, which, as a consequence acts by respectively adding or subtracting.
Compound excitation presents some advantages, such as, for example, simplicity and low-cost of the construction and the relative easiness of machine excitation, even with the low voltages generated by the residual induction, however said excitation does not insure satisfactory performance, particularly because of some functional conditions: in fact, the voltage stability is rather poor when the number of revolutions changes and even when the cos .phi. of the load changes; besides, it is not always easy to obtain parallel performances between alternators being thus excited.
The mixed excitation by means of compound and electronic regulation acting in subtraction presents some relevant drawbacks since, in the case of a malfunction of the electronic regulator, the voltage of the alternator increases and it is no longer possible to lower it. In the case of an electronic regulator which compensates by adding to the compound, the regulator itself must be dimensioned so that it can withstand the overloads of the machine, so that its construction becomes rather costly; besides, should a malfunction of the regulator occur, the same type of drawbacks as occur because of insufficient dimensioning of the compound excitation would present themselves.